Efficient and economical production of plywood demands consistent production of veneer of consistently high quality. Economical veneer production demands the reliable ability of a veneer lathe to cut the greatest possible amount of high quality veneer from each block. Every additional spiral layer or wrap of veneer which can be cut from a given block adds a significant increase to the amount of veneer produced. Such an increase is even more significant in relation to the total size of a block whose initial diameter is small.
The most desirable veneer for use in manufacturing plywood is of a uniform thickness, is free from splits which extend entirely through the thickness of the veneer, and knots in the wood are held securely in place by the surrounding grain. The ability to produce veneer of high quality from each log or block of wood depends to a great degree on maintenance of spatial relationships between several different relatively movable parts of a veneer lathe, and the ability to control these relationships closely in a very dynamic environment where great forces are encountered.
The block from which veneer is "peeled" reacts differently at different times during the process of cutting the veneer. Several factors which apparently affect the resulting veneer quality vary or are likely to vary as the block diameter is reduced during peeling or among different blocks. Among these factors are:
(1) the radius at which the veneer is being cut from the block; PA1 (2) the species of wood of which the veneer is being cut; PA1 (3) the structure of the grain of the particular block, that is, whether the wood has many or few knots, or tight or open grain (depending on whether the growth of the particular part of the tree was fast or slow, often differing between north and south sides of a tree); PA1 (4) the moisture content of the block, which is preferably high at the time veneer is cut from a block; PA1 (5) the temperature of the block, preferably in the range of 150.degree.-165.degree. F.; PA1 (6) the beam strength of the block, that is, its resistance to bending between the spindles of a lathe in response to gravity or the pressure of the veneer knife; and PA1 (7) the position of the block relative to the assumed position of the spindles of the lathe (the spindles may sag or the block may shift downward relative to the spindles because of its own weight when the block is large, or the block may rise in reaction against the upward support provided by the veneer knife and the driving force of the spindles when removal of wood has reduced the weight of the block.
The veneer produced by veneer lathes embodying the previously available technology has been undesirably inconsistent in thickness, primarily as a result of a lack of ability to hold the veneer knife securely and accurately enough in the optimum position and the inability to coordinate the rate of movement of the veneer knife toward the axis of rotation of the block accurately enough with respect to the rate of spindle rotation speed while cutting veneer from the block.
The veneer knife edge height and veneer knife blade pitch angle in the past have often been established as compromises, and have been difficult to maintain accurately during lathe operation. This has resulted in unnecessary failure to achieve the highest economy in production of veneer from each block, as block spinouts occur more frequently when knife height and pitch are improper.
Because it has not been possible to produce veneer whose thickness is consistent enough, it has been necessary to cut veneer somewhat thicker than the preferred thickness in order to ensure that there is sufficient total thickness of veneer to produce plywood whose thickness is within specification. Additionally, the uneven thickness of veneer has required the use of pressure on the plywood as high as 250-450 lb/in.sup.2 in clamping the layers of veneer and glue together to assure tight bonds in the plywood. As a result of such higher clamping pressure the veneer is actually compressed during the process of lamination. Uneven thickness of veneer thus results in a substantial loss of veneer thickness by crushing, a need to sand away considerable amounts of wood to reduce the finished plywood to specified thickness, or both of the above. It is desirable, then, to produce veneer of a more consistent thickness so that the maximum thickness may be reduced without production of veneer thinner than the minimum required.
It is therefore an important objective of the present invention to provide an improved veneer lathe which is capable of production of increased quantities of veneer of consistent thickness and quality from each block.
It is another important objective of the present invention to provide a veneer lathe capable of producing veneer of more accurately controllable thickness than has previously been possible.
It is an important feature of the veneer lathe of the present invention that it includes sensors for directly determining and indicating remotely the positions of various adjustable elements of the veneer lathe, so that the positions of those moveable elements can be adjusted during the operation of the veneer lathe.
It is another important feature of the present invention that it utilizes frequently revised measurement of the amount of travel of the main feed carriage and of the amount of rotation of the spindles to correct the speed at which the main feed carriage is advanced toward the block while peeling veneer.
It is an important advantage of the present invention that it provides a veneer lathe which produces veneer of a more consistent thickness than was possible previously.
It is another important advantage of the present invention that it provides a veneer lathe in which veneer knife movement speed errors are kept from accumulating as veneer thickness errors.
The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.